Yes, you can be banned through the use of mods.
Yes, you can be banned through the use of mods.
It's possible to get banned if you modify a game by adding external code, especially if it violates the developer's terms of service.
It's best not to do that, but it's hard to predict. Steam VAC removed users who used such modifications.
It varies by game, but you can apply glass effects and blue/red skins across many of Valve's titles. Updates with the command SV_PURE will make the game require server textures instead of your own.
As long as those mods don’t interfere with the multiplayer aspect, it should work unless the creators have a solid reason not to let certain features through—like making it simpler to earn achievements.
I'm currently checking it on the Splinter Cell black list. I'm using RadeonPro at the link provided.